Category Archives: Water Quality

Lower Sacramento River Water Temperatures A 5-Year Adaptive Management Study of Lower Sacramento Summer Flows and Water Temperatures

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Nearly three decades ago, state and federal regulators made prescriptions that required the maintenance of water temperatures in the lower Sacramento River below 68oF (20oC) in summer to protect salmon, sturgeon, steelhead, and water quality. The condition was put in water right permits, anadromous fish restoration plans, and in the state’s water quality plan for the basin. Summer is the season when once-abundant spring, fall, and winter run salmon ran up the river and to tributaries to spawn. It is also the rearing season for spring-spawning sturgeon, striped bass, American shad, splittail, and trout, all once abundant in the lower Sacramento River watershed.

The effect of how the prescription was administered in the early 1990’s can be seen in water temperature record for Wilkins Slough in the lower Sacramento River near Grimes (Figure 1). The gradual erosion in the application of the prescription is also apparent over the past two decades. Lack of enforcement of the prescription by federal and state regulating agencies in the last five years is also apparent even in the recent wetter years following the critical drought years of 2013-2015.

I looked at the last five years, 2014-2018, as an adaptive management study to determine how to maintain the 68oF prescription. Plots of water temperatures and river flow from Wilkins Slough (Figures 2-6) are unequivocal evidence that river flow is the primary driver of summer water temperatures in the lower Sacramento River near Wilkins Slough. Air temperature is a lesser factor in summer because it is nearly always warm. A rise in flow over the summer of 2018 (Figure 6) shows clearly that keeping flows in the 6000-8000 cfs range (depending on air temperature) can maintain water temperature near the 68oF target. Flows in the 3000-5000 cfs range lead to water temperatures of 72oF or higher, which are very detrimental to the dependent fish.

Finally, the gradual decline in summer river flow at Wilkins Slough over the past two decades (Figure 7) matches the rise in summer temperatures (Figure 1). It is not a question of changing water quality standards to protect fish. It is simply a question of enforcing the existing standards and water right permit requirements. Increasing Shasta Reservoir releases, limiting water diversions, or some combination thereof, could provide the necessary flows.

Figure 1. Water temperatures recorded at Wilkins Slough in the lower Sacramento River from 1980 to 2018.

Figure 2. Water temperature and river flow at Wilkins Slough May-August 2014.

Figure 3. Water temperature and river flow at Wilkins Slough May-August 2015.

Figure 4. Water temperature and river flow at Wilkins Slough May-August 2016.

Figure 5. Water temperature and river flow at Wilkins Slough May-August 2017.

Figure 6. Water temperature and river flow at Wilkins Slough May-August 2018.

Figure 7. River flow recorded at Wilkins Slough in the lower Sacramento River from 1980 to 2018.

Delta Smelt Summer 2018

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After catching over 800 Delta smelt in 2011 (Figure 1) and near 30 in 2017 (Figure 2), the Summer Townet Survey captured only 3 in 2018 (Figure 3). The pattern is consistent with the spring 20-mm Survey collections

The only option now other than extinction is stocking hatchery smelt in large numbers in their primary summer-fall habitat, the Low Salinity Zone of the Bay-Delta. Release should be near the 2 ppt (3800 EC) location, commonly referred to as X2, which recently has been moving tidally back and forth between Collinsville and Sherman Island in the Sacramento River channel just downstream of the Emmaton gage (Figures 4 and 5). The X2 location has optimum salinity, water temperatures (<70oF), turbidity, and food for Delta smelt.

Figure 1. Summer Townet collections of Delta smelt 2011.

Figure 2. Summer Townet collections of Delta smelt 2017.

Figure 3. Summer Townet collections of Delta smelt 2018.

Figure 4. Water temperature at Emmaton late August 2018. High tide X2 water is 68-69oF.

Figure 5. Salinity (EC) at Emmaton late August 2018. High tide water is near X2 salinity (3800 EC).

“Epic” Salmon Fishing this Summer

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Reports on the July 15 opener on the lower Sacramento fall-run salmon season are good.1 Reclamation and Sacramento River farmers have provided the flows needed to keep water temperatures down (Figure 1), allowing what appears to be a good run up the river from the Golden Gate. Openers in recent years have been poor because of low flows and high water temperatures, as well as low salmon numbers. Numbers are up, and water temperatures are down – good for fishing.

Figure 1. Higher flows in July have cooled the river despite many 100+ degree days. Source.

Winter-Run Salmon Status – 2018

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In a March 14 post, I discussed the primary factor in the initial decline of Sacramento River winter-run salmon in the early 1980s (Figure 1) – higher south Delta exports in drier years after the State Water Project came on line in the 1970s.   In a January 15, 2017 post, I discussed the causes of the recruitment failures from poor egg survival in spawning grounds in summers of 2014 and 2015.  In this post, I suggest that recruitment into the population and long-term population declines stems from fewer spawners (eggs produced) over time and low Sacramento River flows (Shasta Reservoir releases) in fall and winter.

The spawner-recruit relationship (Figure 2) depicts a strong positive effect of the number of spawners on the number of recruits into the population.  This is important because mortality reduces the number of spawners and also the subsequent years’ egg production – a double whammy.  Without mitigation, the population spirals toward extinction.

In addition, the relationship suggests that ten times as many salmon are produced in wetter years as in dry years for the same level of spawners.  Over the past decade, drier years have lower fall and winter river flows in the upper river spawning and early rearing reach (Figure 3), and lower winter flows in the lower river rearing and migratory reach (Figure 4).  The lower fall-winter flows reduce the productive capacity and survival of young salmon in the upper river spawning-rearing reach.  The low winter flows in the lower river reduce transport and survival on the way to and through the Delta.

The road to recovery is to build up the number of spawners by providing better flows in fall and winter, and to ensure eggs are sustained by cold-water Shasta Reservoir releases through the summer.  Hatchery augmentation helps sustain existing low levels of adult spawners in the population; otherwise the population would decline toward extinction in fewer generations.

Figure 1. Spawning population estimates of adult winter-run salmon in the upper Sacramento River from 1974 to 2017. Source: CDFW.

Figure 2. Spawner-recruit (log-log) relationship for the winter-run salmon population in the Sacramento River. The number is the brood year. For example: 1991 depicts the recruits derived from 1991 spawners. Red represents drier years, and blue represents wetter years for the brood year’s first summer and fall. For example: 1991 was a dry year.

Figure 3. Daily average Sacramento River flow below Keswick Dam, 2007-2018. The 54-year average median daily flow is also shown. Source: USGS.

Figure 4. Daily average lower Sacramento River flow at Wilkins Slough, 2008-2018. The 54-year average median daily flow is also shown. Source: USGS.

More on Sacramento River Salmon Declines Reclamation did what it had to do in water years 2010 to 2012, but not in 2016-2018.

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With poor salmon runs from 2009 to 2011, Reclamation provided good conditions in the lower Sacramento River below Shasta Reservoir in spring-summers of 2010 to 2012 for fall-run and winter-run salmon. That effort contributed to recovery of fall-run salmon from the 2007-2009 drought in 2012-2014 (Figure 1). The sequence of below-normal, wet, and below-normal water years (2010-2012) provided sufficient water for good smolt survival, overcoming a significant deficit of adult spawners (eggs spawned). Poor conditions in the subsequent drought of 2013-2015 led to the latest fall-run collapse in 2016-2017.1

So did Reclamation provide good spring-summer conditions in the lower Sacramento River in below-normal, wet, below-normal water year sequence 2016-2018 to help recovery from the latest drought? No. As a result, we can now expect poor runs in 2019 and 2020 instead of a recovery.

2010-2012

Reclamation made a concerted effort in 2010-2012 to meet water temperature objectives in the upper river near Red Bluff (Bend, Balls Ferry, and Red Bluff) and the lower river near Sacramento (Wilkins Slough, Verona). The 56°F and 68°F water temperature objectives for the upper and lower river, respectively, were regularly met (Figures 2-4) in spring and summer.

2016-2018

In a less than concerted effort in 2016-2018, Reclamation has failed to meet the water temperature objectives more often and with greater discrepancies (Figures 5-7). More detail on the failure is provided in a recent post.

Problem and Solution

The causal factor is simply lower flows in spring and summer 2016-2018 than 2010-2012 (Figure 8). Lower flows, higher water temperatures, and lower turbidities lead to poor salmon smolt survival (and low adult migrant survival and subsequent egg viability). A concerted effort to recover salmon would mean maintaining water temperature objectives with spring-summer flows in the lower river at Wilkins Slough in the 7000-8000 cfs range instead of the 5000-6000 cfs range (Figure 8). This may require a supplemental release from Shasta Reservoir as in 2012 (Figure 9), which amounted to nearly 200,000 acre-ft of storage release, so that storage ended at 2,600,000 acre-ft at the end of September. The target end-of-September storage in below-normal water year 2018 is 2,300,000 acre-ft. With water deliveries near 2 million acre-ft from the Sacramento River in 2012 and 2018, a “concerted effort” involving 200 thousand acre-ft to maintain water temperature objectives prescribed in the water right permits seems reasonable. Whether it comes from Shasta storage or water contractor deliveries is a management/permitting agency decision.

Figure 1. Long-term trend in upper Sacramento River fall-run salmon escapement. Red circle denotes recovery from low escapement from 2007-2009 drought.

Figure 2. Water temperature in the upper (Red Bluff, Balls Ferry) and lower Sacramento River (Verona) in 2010. Top red line denotes objective for lower river (68°F); bottom line denotes objective for upper river (56°F). Red circle denotes excessive temperatures. In 2010, a below-normal water year following three years of drought had water temperatures near objectives.

Figure 3. Water temperature in the upper (Red Bluff, Balls Ferry) and lower Sacramento River (Verona) in 2011. Top red line denotes objective for lower river (68°F); bottom line denotes objective for upper river (56°F). In 2011, a wet water year had water temperatures near objectives.

Figure 4. Water temperature in the upper (Red Bluff, Balls Ferry) and lower Sacramento River (Verona) in 2012. Top red line denotes objective for lower river (68°F); bottom line denotes objective for upper river (56°F). Red circles denote excessive temperatures. In 2012, a below-normal water year following a wet year had water temperatures near objectives.

Figure 5. Water temperature in the upper (Red Bluff, Bend, Balls Ferry) and lower Sacramento River (Wilkins Slough, Verona) in 2016. Top red line denotes objective for lower river (68°F); bottom line denotes objective for upper river (56°F). Red circles denote excessive temperatures. In 2016, a below-normal water year following three drought years had water temperatures exceeding objectives April through July.

Figure 6. Water temperature in the upper (Red Bluff, Bend, Balls Ferry) and lower Sacramento River (Wilkins Slough, Verona) in 2017. Top red line denotes objective for lower river (68°F); bottom line denotes objective for upper river (56°F). Red circles denote excessive temperatures. In 2017, a wet water year had water temperatures exceeding objectives May through August.

Figure 7. Water temperature in the upper (Red Bluff, Bend, Balls Ferry) and lower Sacramento River (Wilkins Slough, Verona) in 2018. Top red line denotes objective for lower river (68°F); bottom line denotes objective for upper river (56°F). Red circles denote excessive temperatures. In 2018, a below-normal water year following three drought years had water temperatures exceeding objectives April through June.

Figure 8. Summer flow in the lower Sacramento River (Wilkins Slough) in 2010-2012 and 2016-2018.

Figure 9. Releases of water from Keswick Reservoir to the lower Sacramento River in 2012 compared to 54 year average.